In most cases I prefer characters leveling up as they are used. Someone did a conversation roll (intimidate/persuade etc) - they get a bonus, picked a lock? Bonus, killed something - bonus. Course when you're just getting XP from quests this could get harder, unless you give specific bonusses to the partymember who completed objective X from a quest. I dislike the "whole party levels up at once" deal, it happens in Dragon Age 2 for example, and what happens is that I end up switching my team around every once in a while just to level these guys up and stick them back on the shelve again cause I prefer not using them =P If that means that I'll have a few weaker guys cause I didn't use them - well if I needed them I'd use them more, else its all on me. In which case I'd be thinking about an XCOM - enemy unknown or Fire Emblem type deal, where if you leave a bunch of guys low level and you need them later on, well thats kinda your own fault.